Silicate-containing alkaline compositions for cleaning microelectronic substrates

ABSTRACT

A method and composition for removing sodium-containing materials such as photoresist from microcircuit substrate material utilizes 1,2-Diaminocyclohexanetetracarboxylic Acid in an organic solvent.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention is in the field of removing photoresist andother materials from microcircuit substrates in the manufacture ofintegrated circuits.

[0003] 2. Description of Background Art

[0004] An integral part of microelectronic fabrication is the use ofphotoresists to transfer an image from a mask or reticle to the desiredcircuit layer. After the desired image transfer has been achieved, thephotoresist is removed by stripping before proceeding to some subsequentprocess step.

[0005] Contamination by mobile ions, especially by sodium ions, isresponsible for many failures of integrated circuits, especially duringhigh temperature operation bias burn-in tests. Mobile ion contaminationmay be introduced at various stages during integrated circuitfabrication.

[0006] Those concerned with the development of integrated circuittechnology have continuously sought for materials and techniques toreduce mobile ion contamination. In U.S. Pat. No. 5,417,802, crownethers were used to sequester Group I and Group II ions in organicsolvents used for photoresist removal.

SUMMARY OF THE INVENTION

[0007] In accordance with the present invention, a method andcomposition are provided for stripping sodium-containing material, suchas photoresist. The stripping composition comprises1,2-Diaminocyclohexanetetracarboxylic Acid (CYDTA) in an organicsolvent. The method of the invention comprises contacting said substratewith said stripping composition.

DETAILED DESCRIPTION OF THE INVENTION

[0008] The organic solvents used in photoresist removal and post-metaletch cleaning are a common source of mobile ion contamination. Typicalsolvents include blends of primary and secondary amines and other inertsolvents such as dimethylsulfoxide and dimethylacetamide. These solventsare usually stored in plastic (for example, high density polypropylene)containers. The manufacture of these plastic containers involves the useof inorganic catalysts, which may contain sodium. Consequently, when thesolvents are stored in these plastic containers, sodium can leach intothe solvent. The concentration of sodium in the solvent increases withthe duration of contact with the plastic.

[0009] It has been discovered that 1,2-DiaminocyclohexanetetracarboxylicAcid (CYDTA), which coordinates well with sodium ions, inhibits theadsorption of sodium to integrated circuit surfaces. The addition of1,2-Diaminocyclohexanetetracarboxylic Acid to organic solventsconventionally used in either photoresist removal or post-metal etchclean-up has been found to significantly reduce the concentration ofsodium found on the surface of the resulting cleaned integratedcircuits.

[0010] Experiments using titanium nitride deposited on siliconsubstrates and inspected with secondary ion mass spectroscopy (SIMS)indicate that the addition of 1,2-Diaminocyclohexanetetracarboxylic Acidto such conventional organic solvent formulations as ALEG-310®, aregistered trademark of Mallinckrodt Baker Incorporated of Phillipsburg,N.J., significantly reduced the surface sodium concentrations of thesesubstrates. Direct comparison to parallel treatments with the previouslydisclosed crown ethers showed that the present invention resulted inmuch lower sodium concentrations on the resulting cleaned surfaces.

[0011] In a typical application, a patterned photoresist may be removedfrom etched oxide, metal or semiconductor substrate features using anorganic solvent modified by the addition of1,2-Diaminocyclohexanetetracarboxylic Acid, thereby reducing the extentof sodium contamination of the resulting integrated circuit.Alternatively, the photoresist may be partially removed by exposure toan oxygen plasma and the resulting unwanted residues further removedusing the present invention.

[0012] One embodiment utilizes a stripping solvent, a nucleophilicamine, a non-nitrogen containing weak acid in an amount sufficient topartially the nucleophilic amine such that the stripping composition hasan aqueous pH, when diluted with about 10 parts of water, of about 9.6to about 10.9, said weak acid having a pK value in aqueous solution of2.0 or greater and an equivalent weight of less than 140, and1,2-Diaminocyclohexanetetracarboxylic Acid, whereby said strippingcomposition is able to strip unwanted photoresist or photoresistresidues with minimal increases in the surface sodium concentration ofthe cleaned integrated circuit.

[0013] The non-nitrogen containing weak acids that may be employed inthis invention include organics such as carboxylic acids or phenols aswell as salts of inorganic acids such as carbonic or hydrofluoric acid.

[0014] By weak acids is meant acids having a strength expressed as a“pK” for the dissociation constant in aqueous solution of at least 2.0or higher, preferably 2.5 or higher. Particularly useful are weak acidsof pK>2.0 and preferably having an equivalent weight of less than about140. As examples of such non-nitrogen containing weak acids useful inthis invention there may be mentioned, for example, carboxylic acidssuch as acetic acid, phthalic acid, phenoxyacetic acid and the like,organic acids such as 2-mercaptobenzoic acid, 2-mercaptoethanol and thelike, phenols generally having pK in the range of from 9 to 10, such asphenol, 1,3,5-trihydroxybenzene, pyrogallol, resorcinol,4-tert-butylcatechol and the like, and inorganic acids such as carbonicacid, hydrofluoric acid and the like. The amount of weak acid employedin the stripping compositions of this invention is from about 0.05% toabout 25% by weight of said composition and is present in an amount toneutralize about 19% to about 75% by weight of the amine present in thestripper composition thereby resulting in an aqueous rinse pH for saidstripper compositions of from about pH 9.6 to about 10.9.

[0015] Alkaline stripper components that may be used in this inventionalso cover a wide range of structural types. Their dissociationconstants, once again expressed as pK values, range from about 9 to 11for the beta-oxygen or -nitrogen substituted amines to 8.3 for thesecondary amine, morpholine and hydroxylamines and hydroxylaminederivatives of somewhat lower pK values. Among the alkaline componentsthat may be used there may be mentioned, nucleophilic amines, preferablyfor example, 1-amino-2-propanol, 2-(2-aminoethoxy)ethanol,2-aminoethanol, 2-(2-aminoethylamino)ethanol,2-(2-aminoethylamino)ethylamine and the like. More important than theactual pK value of an amine is its nucleophilicity which should be high.The amount of amine component employed in the stripping compositions ofthis invention is from about 1% to about 50% by weight of saidcomposition.

[0016] It is believed that the interaction of these alkaline strippercomponents with the range of weak acids used in this invention isessentially reversible:

alkaline component+acid⇄salt-like complex.

[0017] Because of the reversibility of this reaction, substantialconcentrations of the alkaline component would remain available duringthe stripping process even though much of the alkaline component hasbeen neutralized from a stoichiometric point of view. This would accountfor the surprisingly rapid stripping rates that are observed even in thepresence of these acids.

[0018] The photoresist stripping compositions of this invention comprisean organic solvent system. The organic solvent system is one having asolubility parameter of from about 8 to about 15, obtained by taking thesquare root of the sum of the squares of the three Hansen solubilityparameters (dispersive, polar and hydrogen bonding). The solvent systemmay comprise any of a number of individual solvents or a mixture ofseveral different solvents. As example of such solvents there may bementioned, various pyrrolidinone compounds such as 2-pyrrolidinone,1-methyl-2-pyrrolidinone, 1-ethyl-2-pyrrolidinone,1-propyl-2-pyrrolidinone, 1-hydroxyethyl-2-pyrrolidinone,1-hydroxypropyl-2-pyrrolidinone, and the like, diethylene glycolmonoalkyl ethers such as those of the formula HOCH₂CH₂—O—CH₂CH₂—O—Rwhere R is an alkyl radical of from 1 to 4 carbon atoms, compoundscontaining sulfur oxides such as dialkyl sulfones of the formula

[0019] where R¹ and R² are alkyl of 1 to 4 carbon atoms, dimethylsulfoxide (DMSO), tetrahydrothiophene-1,1-dioxide compounds of theformula

[0020] wherein R³ is hydrogen, methyl or ethyl, such as sulfolane,methyl sulfolane and ethyl sulfolane, as well as polyethylene glycols,dimethylacetamide or dimethylformamide. The solvent system portion ofthe stripper compositions of this invention will generally comprise fromabout 50% to about 98% by weight of the composition, preferably about85% to about 98% by weight.

[0021] Preferred solvents are N-alkyl-2-pyrrolidinones, such asN-methyl, N-ethyl-, N-propyl-, and N-(2-hydroxyethyl)-,Dimethylsulfoxide, Dimethylacetamide and Dimethylformamide.

[0022] Particularly preferred solvents are N-methyl-2-pyrrolidinone andtetrahydrothiophene-1,1-dioxide.

EXAMPLE

[0023] One thousand grams of a stripper solvent containing about 50parts of N-methyl-2-pyrrolidinone, about 10 parts oftetrahydrothiophene-1,1-dioxide, about 25 parts of 2-aminoethanol, about5 parts of 1,2-dihydroxybenzene, and about 10 parts of water wereweighed into a fluoropolymer beaker. The additives,1,2-Diaminocyclohexanetetracarboxylic Acid or 18-Crown-6, were weighedout and dissolved in the stripper solvent as needed. The solution wasthen raised to the desired temperature and a titanium nitride (TiN)coated wafer was placed in the solution for twenty minutes, removed andrinsed with DI water and analyzed using SIMS. All experiments werecarried out in a class 100 clean room taking extra care to preventsodium contamination of the wafer.

[0024] Three wafers were subjected to the water rinsing and drying steponly to establish a baseline sodium value without any stripper solventtreatment. The unmodified stripper solvent was tested at 65C and 85C fortwenty minutes to determine the relative sodium levels left behind onthe TiN surface by this process. Results are shown in Table 1. For thesecond set of experiments, 0.1 weight percent of1,2-Diaminocyclohexanetetracarboxylic Acid Monhydrate (CYDTA) was addedto the stripper solvent. For the third set of experiments the weightpercent of 1,2-Diaminocyclohexanetetracarboxylic Acid Monhydrate wasincreased to 0.5%. For the fourth set of experiments the weight percentof 1,2-Diaminocyclohexanetetracarboxylic Acid Monhydrate was increasedto 0.9%. In the fifth set, 0.1 weight percent of 18-Crown-6 was added tothe stripper solvent and tested at 45C, 65C and 85C.

[0025] These data (Table 1) clearly show that the addition of1,2-Diaminocyclohexanetetracarboxylic Acid to the stripper solventresults in much lower sodium surface concentrations than the unmodifiedsolvent. Crown ether addition had no beneficial effect. TABLE 1Treatment Relative Surface Sodium Process Temperature Concentration(using SIMS) Water rinse and dry (untreated) 0.0052, 0.0046, 0.0051Stripper solvent only 65 C. 0.16 85 C. 0.25 Solvent + 0.1% CYDTA 65 C.0.04 85 C. 0.07 Solvent + 0.5% CYDTA 65 C. 0.02 85 C. 0.05 Solvent +0.9% CYDTA 65 C. 0.03 85 C. 0.04 Solvent + 0.1% 18-Crown- 45 C. 0.33 665 C. 0.41 85 C. 0.45

1. A method of stripping sodium-containing material from a microcircuitsubstrate, comprising contacting said substrate with a strippingcomposition comprising 1,2-Diaminocyclohexanetetracarboxylic Acid(CYDTA) in an organic solvent.
 2. The method of claim 1, wherein saidsodium-containing material is photoresist.
 3. The method of claim 1,wherein said stripping composition further comprises a nucleophilicamine, a non-nitrogen containing weak acid in an amount sufficient topartially the nucleophilic amine such that the stripping composition hasan aqueous pH, when diluted with about 10 parts of water, of about 9.6to about 10.9, said weak acid having a pK value in aqueous solution of2.0 or greater and an equivalent weight of less than 140, whereby saidstripping composition is able to strip unwanted photoresist orphotoresist residues with minimal increases in the surface sodiumconcentration of the cleaned integrated circuit.
 4. The method of claim1, wherein: the stripping solvent is a stripping solvent system having asolubility parameter of from about 8 to about 15 and is present in anamount of from about 50% to about 98% by weight of the strippingcomposition; and the nucleophilic amine is present in an amount of fromabout 1 to about 50% by weight of the stripping composition.
 5. Themethod of claim 4, wherein the weak acid is present in the strippingcomposition in an amount of from about 0.05% to about 25% by weight ofsaid stripping composition.
 6. The method of claim 5, wherein the weakacid has a pK of 2.5 or higher.
 7. A stripping composition for carryingout the method of claim 1, comprising1,2-Diaminocyclohexanetetracarboxylic Acid (CYDTA) in an organicsolvent.
 8. The composition of claim 7, further comprising anucleophilic amine, a non-nitrogen containing weak acid in an amountsufficient to partially the nucleophilic amine such that the strippingcomposition has an aqueous pH, when diluted with about 10 parts ofwater, of about 9.6 to about 10.9, said weak acid having a pK value inaqueous solution of 2.0 or greater and an equivalent weight of less than140, whereby said stripping composition is able to strip unwantedphotoresist or photoresist residues with minimal increases in thesurface sodium concentration of the cleaned integrated circuit.
 9. Thecomposition of claim 7, wherein the stripping solvent is a strippingsolvent system having a solubility parameter of from about 8 to about 15and is present in an amount of from about 50% to about 98% by weight ofthe stripping composition; and the nucleophilic amine is present in anamount of from about 1 to about 50% by weight of the strippingcomposition.
 10. The composition of claim 9, wherein the weak acid ispresent in the stripping composition in an amount of from about 0.05% toabout 25% by weight of said stripping composition.
 11. The compositionof claim 10, wherein the weak acid has a pK of 2.5 or higher.
 12. Analkaline-containing photoresist stripper according to claim 9, whereinthe weak acid is 1,2-dihydroxybenzene.
 13. An alkaline-containingphotoresist stripper according to claim 12, wherein the amine is2-aminoethanol.
 14. An alkaline-containing photoresist strippercomposition comprising on a weight basis: from about 50% to about 98% ofa stripping solvent having a Hansen solubility parameter of from about 8to about 15, from about 1% to about 50% by weight of a nucleophilicamine, from about 0.05% to about 25% by weight of a non-nitrogencontaining weak acid having a pK value in aqueous solution of 2.0 orgreater, and equivalent weight of less than 140 and present in thestripping composition in an amount to partially neutralize thenucleophilic amine such that the stripping composition has an aqueouspH, when diluted with about 10 parts of water, of about 9.6 to about10.9, and from about 0.01% to 5% of1,2-Diaminocyclohexanetetracarboxylic Acid.
 15. An alkaline-containingphotoresist stripper according to claim 14, wherein the weak acid is1,2-dihydroxybenzene.
 16. An alkaline-containing photoresist stripperaccording to claim 14, wherein the amine is 2-aminoethanol.
 17. Analkaline-containing photoresist stripper according to claim 13, whereinthe stripping solvent is N-methyl-2-pyrrolidinone and/ortetrahydrothiophene-1,1-dioxide and may contain up to 20% of water. 18.An alkaline-containing photoresist stripper according to claim 16,wherein the stripping solvent is N-methyl-2-pyrrolidinone and/ortetrahydrothiophene-1,1-dioxide and may contain up to 20% of water. 19.An alkaline-containing photoresist stripping composition comprising on aweight basis from about 50% to about 98% of N-methyl-2-pyrrolidinone,from about 1 to about 20% of tetrahydrothiophene-1,1-dioxide, from about1 to about 20% of water, from about 1 to about 50% of 2-aminoethanol,from about 0.05% to about 25% of 1,2-dihydroxybenzene present in anamount whereby the amine is neutralized such that the strippingcomposition has an aqueous pH, when diluted with about 10 parts ofwater, of about 9.6 to about 10.9, and about 0.01% to 5% of1,2-Diaminocyclohexanetetracarboxylic Acid.
 20. A photoresist strippingcomposition comprising a stripping solvent and1,2-Diaminocyclohexanetetracarboxylic Acid.